Question

ActiveRecord offers attribute helper methods such as _? and the “dirty” methods (_changed? etc.)

Is there a Rails way to define these same methods on non-persisted or “virtual” attributes?

I’m hoping for something like:

class MyClass < ActiveRecord::Base

  some_macro :my_attribute

end


$ @my_class = MyClass.new
$ @my_class.my_attribute? # => false
$ @my_class.my_attribute_changed? # => false

Answer 1

Well this was certainly something interesting to investigate. Apparently there is not a straight forward way to do this… here are two things I found

From 2009

From 2011 – reinforces the 2009 post but makes it a bit cleaner. You create a module that updates the attribute hash. From the Brandon Weiss post:

# app/models/dirty_associations.rb
module DirtyAssociations
  attr_accessor :dirty

  def make_dirty(record)
    self.dirty = true
  end

  def changed?
    dirty || super
  end
end

# app/models/lolrus.rb
class Lolrus
  include DirtyAssociations

  has_and_belongs_to_many :buckets,
                          :after_add    => :make_dirty,
                          :after_remove => :make_dirty
end

There is also this plugin mentioned here but I am not sure how useful it is for you.